摘要
基于双功能催化剂的CO2加氢耦合甲苯甲基化直接合成对二甲苯(p-xylene,PX)工艺具有原子经济性、可实现绿氢储存和有效利用CO2等优点,该工艺尚未有完整的流程设计和优化策略等技术经济分析.该研究基于CO2加氢耦合甲苯甲基化的选择催化结果,选取了高转化率、高二甲苯选择性和高PX选择性等3种甲基化催化剂及其实验结果,进行PX生产工艺流程设计与模拟.结果表明,在获得相同PX产量的基础上,高PX选择性催化剂工艺单位PX产品的原料消耗量仅为其他2种催化剂工艺的72.6％和58.9％;高二甲苯选择性催化剂工艺原料消耗率较高,并且具有最高的能耗,但借助异构化技术可实现最大PX生产潜力,展现了最优经济性.基于双功能催化剂的CO2加氢耦合甲苯甲基化直接合成PX工艺可提高CO2转化率、降低物料循环能耗,进一步提高二甲苯和PX选择性将极大地提升工艺的技术经济性.
Abstract
[Objective]p-Xylene(PX)is an important aromatic product with the highest consumption among xylene isomers.It is widely used as a raw material for upstream production of several important chemical products.Carbon dioxide(CO2)is a major gas responsible for the greenhouse effect.Furthermore,in addition to methanol,CO2 and syngas also show great technical potential as methylation agent.The direct synthesis of PX by CO2 hydrogenation coupled with toluene methylation over a bifunctional catalyst has the advantages of atomic economy,green hydrogen storage,and CO2 utilization,but a complete techno-economic evaluation of process design and optimization strategy has not been performed.[Methods]Based on the selective catalytic results of CO2 hydrogenation coupled with toluene methylation,three toluene methylation catalysts with high conversion,high xylene selectivity,and high PX selectivity and their experimental results were chosen,and the process flow of PX production by CO2 hydrogenation coupled with toluene methylation was designed and simulated by software.The following was the process flow:the raw materials of the reaction were pretreated and compressed into the reactor,the reaction products were flashed four times to separate the gas from the liquid,some raw materials were circulated,and the liquid products were sequentially separated or purified to yield benzene,PX,o-xylene,and heavy aromatic hydrocarbons.Moreover,because of the various catalysts,RStoic,a stoichiometric reactor module,was employed to model the methylation reaction unit.Based on the characteristics of different catalysts,the conversion rate of each reactant was specified.Furthermore,based on controlling the same PX output,the raw material feed ratio of the reactor was also specified,and the xylene isomer was separated by reactive distillation.[Results]Analysis of the raw material cost,equipment cost,and energy consumption of the process flow corresponding to the three catalysts was conducted,and the results showed that the raw material of the unit PX product of the high-PX-selectivity catalyst process was only 72.6％and 58.9％of those of the other two catalyst processes and theCO2 consumption of the unit PX product was 27.3％and 44.7％of that of the other two catalyst processes.However,the high-xylene-selectivity catalyst process could yield more PX production through isomerization technology,and its energy consumption was also the lowest.Because reactive distillation was employed as the post-separation of xylene isomerization products,the high-xylene-selectivity catalyst process had a high raw material consumption rate and the highest energy consumption,but by isomerization technology,it had the highest PX production potential and showed the best economy through economic accounting of different PX production processes.[Conclusions]CO2 hydrogenation coupled with toluene methylation technology can enhance the conversion rate of raw materials,reduce the energy consumption of material circulation,and enhance the xylene and PX selectivities,which will greatly improve its technical economy.Furthermore,the production process with high PX selectivity is a green chemical process with broad development prospects for reducing carbon emissions in the environment,achieving carbon cycle,energy conservation,and emission reduction.
基金项目
甘肃省基础研究创新群体项目(22JR5RA219)
国家自然科学基金联合基金(U22A20415)
万方数据